The accuracy of medication delivery is critical, since minor differences in medication quantity can dramatically affect the health of a patient. Thus, safeguards must be designed into the delivery system to protect the patient from over or under delivery of medication. For example, in the case where insulin is administered via an infusion device to a diabetic patient, excessive insulin delivery could cause complications due to hypoglycaemia, and possibly even result in death. Therefore, controlled delivery with safeguards against over delivery of medications is required for infusion devices.
Safeguards against over delivery have been incorporated into electronic controllers of infusion pumps in varying ways. For example, the controller may comprise a microprocessor that monitors motor current consumption to detect a malfunction or utilize sensors for occlusion detection or the like. However, a malfunction of the controller itself, for example a direct short from the power source to the pump motor, might cause the pump motor to drive continuously and deliver all the medication contained in the infusion system over a short period and thereby cause severe over delivery.
To guard against such a malfunction US 2002/0071225 A1 teaches to provide infusion devices with a safety circuit system that this designed to cause a disconnection of a drive motor of the pump when the controller fails.
To increase the operational safety of infusion devices it is also known to use solenoid actuators or stepper motors to drive the infusion pump. Although in this way the risk of a continued infusion in case of a controller failure may be significantly reduced, solenoid actuators or stepper motors are rather expensive and not nearly as energy efficient as DC motors. Large energy consumption is a serious disadvantage as larger and heavier batteries are required which is incompatible with the standard design objective to make infusion devices small, compact and light-weight.